class Solution {
public:
    int numberOfArithmeticSlices(vector<int>& nums) {
        int n=nums.size();
        vector<int> dp(n);
        int ret=0;
        for(int i =2;i<n;i++)
        {
            dp[i] = nums[i]-nums[i-1]==nums[i-1]-nums[i-2]?dp[i-1]+1:0;
            ret+=dp[i];
        }
        return ret;
    }
};